Pneumatic sound generators usually comprise a housing with an inlet for air under pressure and a plenum chamber bounded by a membrane. The latter, when set in oscillation, intermittently opens an escape path to a resonator in the form of a horn or cornet whose tubular body has a mouthpiece secured to the housing and encloses a vibrating air column which determines the frequency of the emitted sound. Several such cornets may be used conjointly for multi-tone signaling.
The quality of the sound depends in large measure on the absence of leaks through which air could escape from the column. Thus, it is important to form an airtight junction between the housing and the mouthpice of the cornet. Though this mouthpiece could be an integral part of the housing which is threadedly or adhesively secured to the body of the cornet upon assembly, it is often more convenient to manufacture the housing separately. A threaded connection, in any event, is costly and also introduces an element of uncertainty since the pressure exerted during assembly determines the extent of interengagement and, with it, the calibration of the instrument. Such calibration can be carried out by other means, e.g. as disclosed in my prior U.S. Pat. No. 4,135,473, so that an invariable fit is desirable. The use of an adhesive, on the other hand, may leave unsightly deposits at the outer joint surface and/or a residue at the inside impairing the tonal quality. Moreover, the polymerization or setting time of the usual adhesives is rather long, thus delaying for a considerable period the use of a freshly assembled sound generator.